The present invention relates to the field of hand-held vacuum pumps, particularly of the type disclosed in U.S. Pat. Nos. 3,612,722, 4,775,302 and 4,806,084, by the present inventor Theodore C. Neward, the disclosures of which are incorporated herein by reference.
Vacuum pumps are generally useful whenever a vacuum is desired, for example, to provide suction. Many types of vacuum pumps have been devised, but they often suffer from such drawbacks as complexity, expense, excessive bulk, inability to pull a suitable vacuum, and the like. The vacuum pump of the aforesaid patents has significantly solved the need for a vacuum pump which is simple, inexpensive, lightweight, compact and portable, and one which can pull a useful vacuum.
Such hand-held vacuum pumps are particularly useful in various industries, such as the automotive industry for vacuum system testing and repair, liquid sampling and the like. In the medical field, for example, such pumps have been used with vacuum extraction devices in childbirth, an aid for testing for throat blocking of choking victims, and other uses. Vacuum pumps manufactured according to the aforesaid patents have the ability to pull a vacuum of, for example, twenty-eight inches of mercury.
In some applications for such vacuum pumps, it is particularly desirable to pull a preset or controlled vacuum, and one which is repeatable. Inasmuch as the hand-held vacuum pump is manually operated by hand and because the pump can quickly pull a relatively high vacuum, it is difficult to manually pull a given level of vacuum.